What are PDA advantages compared to regular GPS receiver?

Aside from being cool, a PDA might make sense for you as part of a personal navigation system for a number of reasons. Some of the advantages include

• Larger screens: PDAs have larger, higher-resolution, color screens compared with handheld GPS receivers. This is a big plus if your eyesight isn’t as good as it used to be — and it’s really important if you’re using the PDA while driving. You want to be able to quickly glance at a map on the screen, determine your location, and then get your eyes back on the road.
• More maps: Most of the maps that you can upload to GPS receivers don’t have a lot of detail; especially the topographic maps. These maps tend to be vector line maps and don’t have the resolution or detail found on paper maps that you’d use for hiking. Several mapping programs are available for PDAs that support all types of maps, and you can even create your own custom maps. With a PDA, you can use more detailed maps, like scanned, color 1:24,000 topographic maps. Bonus: You’re not locked in to using only a GPS receiver manufacturer’s proprietary software and maps.
• Expandable memory: Unlike many GPS receivers, which have fixed amounts of memory, most PDAs support expandable memory with plug-in memory cards. The only limitation to the number of the maps and amount of data that you can store is the size of the memory card.
• Usability: Although handheld GPS receivers are fairly easy to use, the user interfaces found on PDAs are even simpler. Using a touch screen and stylus to enter data and commands is a lot faster and easier than using the buttons on a handheld GPS receiver.
• Custom programs: Developers can easily write custom programs for PDAs that access the data output from a GPS receiver. If you’re collecting information that’s based on location data, this can make your job much easier than pressing buttons on a GPS receiver and then handwriting remarks in a field notebook.
• PDA features: PDAs have all sorts of useful programs such as address books, contact lists, and databases designed for readily storing data. A fair amount of this information tends to be location based (like addresses), and having a single information/navigation device is the definition of practical.